1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a scheduling method and an apparatus supporting the same in a wireless local area network (WLAN) system.
2. Related Art
Recently, diverse wireless communication technologies are under development in line with the advancement of information communication technology. Among them, a wireless local area network (WLAN) is a technique allowing mobile terminals such as personal digital assistants (PDAs), lap top computers, portable multimedia players (PMPs), and the like, to wirelessly access the Internet at homes, in offices, or in a particular service providing area, based on a radio frequency technology.
Since IEEE (Institute of Electrical and Electronics Engineers) 802, a standardization organization of a WLAN technique, was established in February 1980, a great deal of standardization works have been conducted.
The early WLAN technique supported the rate of 1˜2 Mbps through frequency hopping, spread spectrum, infrared communications, and the like, by using a 2.4 GHz frequency based on IEEE 802.11, and recently, a maximum rate of 54 Mbps can be supported by employing orthogonal frequency division multiplex (OFDM) technology to the WLAN. Further, IEEE 802.11 are putting standards of various techniques, such as improvement of quality of service (QoS), allowing for compatibility of access point (AP) protocols, achievement of security enhancement, measurement radio resource measurement, wireless access vehicular environment, ensuring fast roaming, establishing a mesh network, interworking with an external network, wireless network management, and the like, into practical use or are still developing them.
A basic access mechanism of an IEEE 802.11 MAC (Medium Access Mechanism) is a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) combined with binary exponential backoff. The CSMA/CA mechanism is also called a DCF (Distributed Coordination Function) of IEEE 802.11 MAC, basically employing a ‘listen before talk’ access mechanism. In this type of access mechanism, a station (STA) first listens to a radio channel or a medium before starting a transmission. Upon listening, when it is detected that the medium is not in use, the listening station starts its transmission. Meanwhile, when it is detected that the medium is in use, the station enters a delay period determined by a binary exponential backoff algorithm, rather than starting its transmission.
A station which has accessed a channel through the foregoing channel access procedure may obtain authority to use a wireless medium and transmit its frame. Here, when a plurality of frames to be transmitted are buffered in the station, a transmission method including transmission order of frames is required to be considered. A scheduling method that may be able to schedule a transmission schedule of frames and effectively transmit frames in an opportunity for using a limited wireless medium is required.